1. Sign in to Google Calendar.
2. Find an existing event or create a new one.
3. Click the “Find a time” tab.
4. Enter the email addresses of your guests in the box on the right. Remember, your guests will need to have granted you access to their calendar for this to work.
5. Your guests' calendars will appear and you can pick a time that works for everyone. You can compare up to 20 schedules at a time.

Your guests don’t need to be using Google Calendar or Gmail to receive and respond to Google Calendar invitations.